The present invention relates generally to electronic components and electronic component packaging. More particularly, the present invention relates to a method of singulating electronic components from a wafer.
As is well known to those of skill in the art, integrated circuits, i.e., electronic components, are fabricated in an array on a wafer. The wafer is then cut, sometimes called diced, to singulate the integrated circuits from one another.
The surface of a wafer that includes the circuitry or other functional components is called the xe2x80x9cfront-sidexe2x80x9d or xe2x80x9cfirst surfacexe2x80x9d of a wafer and the opposite surface of the wafer, the surface that has no functional components or circuitry, is called the xe2x80x9cback-sidexe2x80x9d or xe2x80x9csecond surfacexe2x80x9d of the wafer. In the prior art, individual integrated circuits were singulated from wafers using either front-side or back-side cutting.
FIG. 1 is a cross-sectional view of a section of a wafer 10 being cut from a front-side surface 10F of wafer 10 in accordance with the prior art using front-side singulation methods. According to prior art front-side singulation methods, integrated circuits 12 were formed in wafer 10 and were delineated by scribe lines 14, which included a first scribe line 14A and a second scribe line 14B, on front-side surface 10F of wafer 10. Scribe lines 14 were formed by methods well known to those of skill in the art. For example, scribe lines 14 were often formed by selective etching of a silicon oxide layer 18 on front-side surface 10F.
To illustrate, first scribe line 14A delineated a first integrated circuit 12A from a second integrated circuit 12B. As shown in FIG. 1, each scribe line 14 had a width WF.
According to prior art front-side singulation methods, a back-side surface 10B of wafer 10 was attached to a tape 20. Wafer 10 was then sawed completely through with a saw blade 22. Saw blade 22 was aligned with scribe lines 14 using an optical alignment system in a well-known manner. In this manner, integrated circuits 12 were singulated. According to prior art methods, tape 20 was used to support wafer 10 during sawing and to support the singulated integrated circuits 12 after sawing was complete.
Using prior art front-side singulation methods, width WF of scribe lines 14 had to be sufficiently large to accommodate: the width of saw blade 22; the inexact positioning and alignment of saw blade 22; the mechanical wobbling of saw blade 22; and the uneven or rough surfaces resulting from the mechanical nature of the cutting using saw blade 22. Stated another way, width WF of scribe lines 14 had to be large enough that the saw cut made by saw blade 22 was always within a scribe line 14. For example, saw blade 22 is within scribe line 14B in FIG. 1.
The optical alignment system of the prior art used scribe lines 14 directly to align saw blade 22 and saw blade 22 was aligned to scribe lines 14 to within a mechanically mandated tolerance. To accommodate this tolerance, and the other factors discussed above that are associated with any sawing processes, scribe lines 14 were made significantly wider than saw blade 22. To illustrate, the typical width of saw blade 22 was between 0.001 inches (0.026 mm) and 0.002 inches (0.051 mm) while width WF of scribe line 14 was typically within the range of 0.003 inches (0.077 mm) to 0.008 inches (0.203 mm).
Disadvantageously, forming scribe lines 14 with relatively large widths WF resulted in less integrated circuits 12 for any given size wafer 10 than could be formed with smaller, more optimal, scribe line widths. This was because larger widths WF meant scribe lines 14 took up more wafer surface 10F area. This, in turn, meant more wasted wafer surface 10F area and less surface 10F area available for integrated circuits 12. Consequently, the integrated circuit 12 yield per wafer 10 decreased. As a result, the cost of each integrated circuit 12 from wafer 10 was increased. Unfortunately, in today""s highly competitive markets it is very important to minimize the cost of each integrated circuit 12 to remain competitive.
In certain instances, such as integrated circuits that include micro-machines or other delicate functional components, it is important to protect the front-side surface of the wafer during sawing from the pressure and shards and particulates generated during sawing. In these instances, prior art back-side singulation methods were used to saw the wafer from the back-side surface of the wafer. However, using prior art back-side singulation methods required even larger scribe line widths and resulted in even lower integrated circuit yield per wafer.
FIG. 2 is a cross-sectional view of a section of a wafer 30 being cut from a back-side surface 30B of wafer 30 in accordance with the prior art. To protect a front-side surface 30F of wafer 30, front-side surface 30F was attached to a tape 32. Tape 32 supported wafer 30 during sawing.
Saw blade 22 was aligned with scribe lines 14-1 on front-side surface 30F of wafer 30 using a two-step process. First, tape 32 was aligned with scribe lines 14-1. Then, front-side surface 30F was attached to tape 32. Tape 32 had a surface area greater than the area of front-side surface 30F such that tape 32 had an exposed region, which extended beyond wafer 30. Tape 32 had alignment marks in the exposed region of tape 32. As an example, see alignment holes 30a and 30b of Roberts, Jr. et al., U.S. Pat. No. 5,362,681, which is herein incorporated by reference in its entirety. In the above manner, scribe lines 14-1 were aligned with the alignment marks of tape 32.
Second, saw blade 22 was aligned with the alignment marks of tape 32. Wafer 30 was then sawed with saw blade 22 from back-side surface 30B. However, since saw blade 22 was aligned indirectly to scribe lines 14-1 using alignment marks of tape 32, a large tolerance, associated with the alignment of saw blade 22 to scribe lines 14-1, was required.
To accommodate this large tolerance, each of scribe lines 14-1 had a relatively large width WB. More particularly, referring now to FIGS. 1 and 2 together, width WB of scribe lines 14-1 of wafer 30, that was designed to be cut from back-side surface 30B, was significantly larger than width WF of scribe lines 14 of wafer 10, which was designed to be cut from front-side surface 10F. To illustrate, width WB was typically at least 0.012 inches (0.305 mm), and often even larger.
As with scribe line 14 discussed above, forming scribe lines 14-1 with relatively large widths WB resulted in less integrated circuits 12 for any given size wafer 30. In the particular case of scribe lines 14-1 on wafer 30 in FIG. 2, the scribe lines 14-1 are even thicker than scribe lines 14 in FIG. 1 and the number of integrated circuits 12 is even less than the corresponding number of integrated circuits 12 formed in the same size wafer 10 in FIG. 1. Consequently, using prior art back-side cutting as shown in FIG. 2 resulted in an even smaller yield of integrated circuits 12 from wafer 30. As a result, the cost of each integrated circuit 12 from wafer 30 was even greater than the cost of each integrated circuit 12 from wafer 10.
As discussed above, both front-side and back-side prior art methods of singulation wasted large amounts of wafers 10 and 30. This waste was necessary, using prior art methods, in order to create scribe lines 14 and 14-1 with widths WF and WB large enough to accommodate: the width of saw blade 22; the inexact positioning and alignment of saw blade 22; the mechanical wobbling of saw blade 22; and the uneven or rough surfaces resulting from the mechanical nature of cutting using saw blade 22.
As also discussed above, forming scribe lines 14 or 14-1 with relatively large widths WF and WB, as required in the prior art, resulted in less integrated circuits 12 for any given size wafer 10 or 30. As a result, the cost of each integrated circuit 12 from wafer 10 or 30 was greater than optimal. This was particularly true when prior art back-side singulation methods were used.
In addition, both the prior art front-side and back-side sigulation processes discussed above include cutting completely through wafer 10 and 30 to singulate integrated circuits 12. Consequently, each integrated circuit 12 must be further processed, shipped and wrapped separately, thus driving up the cost of each integrated circuit 12, increasing the probability of defective units by increasing handling operations and driving down the efficiency of the process.
What is needed is a method for singulating integrated circuits from wafers that does not require the large width scribe lines of prior art methods and therefore increases the yield per wafer and decreases the cost per integrated circuit.
As discussed above, using prior art methods of back-side singulation, scribe lines had to have widths large enough to accommodate: the width of saw blade; the inexact positioning and alignment of saw blade; the mechanical wobbling of saw blade; and the uneven or rough surfaces resulting from the mechanical nature of cutting a using saw blade. As also discussed above, forming the scribe lines with relatively large widths resulted in less integrated circuits for any given size wafer, i.e., a loss of yield. This resulted in a substantial increase in the cost of the integrated circuits.
As discussed in more detail below, according to one embodiment of the invention, a wafer is cut from the back-side surface of the wafer, thus protecting the front-side surface of the wafer and, more particularly, the integrated circuits and/or functional units. However, advantageously, and in direct contrast to the prior art, back-side singulation according to the invention is preformed by a laser. Consequently, according to the invention, no saw blade is used and the width of the scribe lines does not need to be large enough to accommodate: the width of saw blade; the inexact positioning and alignment of saw blade; the mechanical wobbling of saw blade; and the uneven or rough cutting surfaces left by saw blade. Stated another way, using the invention, the width of the scribe lines does not need to be any larger than the width of the beam from the laser plus some minimal tolerance for alignment. Consequently, using the invention, scribe lines typically have widths between 0.0005 inches (0.013 mm) and 0.001 inches (0.026 mm).
This is in stark contrast to the prior art methods of back-side singulation which required scribe lines with widths of at least 0.012 inches (0.305 mm), and often even larger. As a result, using the invention, the width of scribe lines is on the order of twenty-four times smaller than the width of scribe lines required by the prior art methods; a 2400% decrease. Therefore, using the invention, the wafer is cut from back-side surface and the integrated circuits of wafer are protected during singulation while, at the same time, there is minimal waste of wafer and the cost per integrated circuit is significantly lowered.
Equally impressive is the fact that, using the present invention, the width of the scribe lines is six to fourteen times smaller than the width of the scribe lines required using prior art front-side singulation methods. Consequently, the invention is well suited to front-side singulation and represents a significant improvement over prior art front-side singulation methods as well.
In addition, unlike the prior art front-side and back-side sigulation processes discussed above, the method and structure of the invention does not include cutting completely through the wafer to singulate the integrated circuits. Consequently, each integrated circuit can be further processed, shipped and wrapped in a wafer array, thus driving down the cost of each integrated circuit, decreasing the probability of defective units by decreasing handling operations and driving up the efficiency of the process.
In accordance with one embodiment of the present invention, a method includes providing a substrate, the substrate including a substrate first surface and a substrate second surface, opposite the substrate first surface, and a substrate thickness between the substrate first surface and the substrate second surface.
A scribe line is then formed on the substrate first surface, the scribe line including a scribe line width extending in a first direction on the substrate first surface and a scribe line length extending in a second direction, perpendicular to the first direction, on the substrate first surface, the scribe line delineating a first region of the substrate from a second region of the substrate on the substrate first surface.
A laser beam is then aligned on the substrate second surface such that the laser beam is aligned on the substrate second surface with the scribe line on the substrate first surface. A trench is then created in the substrate using the laser.
According to the invention, the trench includes: a trench opening at the substrate second surface, the trench opening including a trench opening width extending in the first direction along the substrate second surface; a trench depth extending from the trench opening to a trench bottom located at a trench bottom position within the substrate, the trench bottom including a trench bottom width extending in the first direction at the trench bottom position within the substrate; first and second trench sides extending from the trench opening to the trench bottom; a trench length extending in the second direction on the substrate second surface and being at least partially coextensive with the scribe line length on the substrate first surface such that the trench is positioned below the scribe line within the substrate and the trench delineates the first region of the substrate from the second region of the substrate on the substrate second surface.
The first region of the substrate is then singulated from the second region of the substrate along the trench.
In accordance with a second embodiment of the present invention, a method includes providing a substrate, the substrate including a substrate first surface and a substrate second surface, opposite the substrate first surface, and a substrate thickness between the substrate first surface and the substrate second surface. A scribe line is then formed on the substrate first surface, the scribe line including a scribe line width extending in a first direction on the substrate first surface and a scribe line length extending in a second direction, perpendicular to the first direction, on the substrate first surface, the scribe line further including a scribe line depth extending into the substrate first surface and a scribe line bottom surface, the scribe line delineating a first region of the substrate from a second region of the substrate on the substrate first surface.
A reflective layer is formed on the scribe line bottom surface. A laser scribe machine is then aligned on the substrate second surface such that a laser beam from the laser scribe machine is aligned on the substrate second surface with the scribe line on the substrate first surface.
A portion of the substrate is then ablated from the substrate second surface using the laser beam, the laser beam ablating the portion of the substrate until the laser beam contacts the reflective layer on the scribe line bottom surface and the laser beam light is reflected from the reflective layer on the scribe line bottom surface. Power to the laser beam is then removed when the laser beam light is reflected from the reflective layer on the scribe line bottom surface, thereby ceasing the ablation of the substrate. In this way, the ablation of the portion of the substrate creates a trench in the substrate second surface.
According to the invention, the trench includes: a trench opening at the substrate second surface, the trench opening including a trench opening width extending in the first direction along the substrate second surface; a trench depth extending from the trench opening to a trench bottom, the trench bottom including a portion of the reflective layer on the scribe line bottom surface, the trench bottom including a trench bottom width extending in the first direction at the reflective layer of the scribe line bottom surface; first and second trench sides extending from the trench opening to the trench bottom; a trench length extending in the second direction on the substrate second surface and being at least partially coextensive with the scribe line length on the substrate first surface such that the trench is positioned below the scribe line within the substrate and the trench delineates the first region of the substrate from the second region of the substrate on the substrate second surface.
The first region of the substrate is then singulated from the second region of the substrate along the trench.
In accordance with a third embodiment of the present invention, a method includes providing a substrate, the substrate including a substrate first surface and a substrate second surface, opposite the substrate first surface, and a substrate thickness between the substrate first surface and the substrate second surface.
A scribe line is then formed on the substrate first surface, the scribe line including a scribe line width extending in a first direction on the substrate first surface and a scribe line length extending in a second direction, perpendicular to the first direction, on the substrate first surface, the scribe line delineating a first region of the substrate from a second region of the substrate on the substrate first surface.
A laser beam is then aligned on the substrate second surface such that the laser beam is aligned on the substrate second surface with the scribe line on the substrate first surface. A trench is then created in the substrate using the laser.
A portion of the substrate is then ablated from the substrate second surface by applying the laser beam to the substrate second surface, thereby creating a trench in the substrate.
According to the invention, the trench includes: a trench opening at the substrate second surface, the trench opening including a trench opening width extending in the first direction along the substrate second surface; a trench depth extending from the trench opening o a trench bottom point located at a trench bottom position within the substrate; first and second trench sides extending from the trench opening to the trench bottom point, such that the trench has a cross section which is approximately triangular in shape; a trench length extending in the second direction on the substrate second surface and being at least partially coextensive with the scribe line length on the substrate first surface such that the trench is positioned below the scribe line within the substrate and the trench delineates the first region of the substrate from the second region of the substrate on the substrate second surface.
The first region of the substrate is then singulated from the second region of the substrate along the trench.
In accordance with a fourth embodiment of the present invention, a method includes providing a substrate, the substrate including a substrate first surface and a substrate second surface, opposite the substrate first surface, and a substrate thickness between the substrate first surface and the substrate second surface.
A scribe line is then formed on the substrate first surface, the scribe line including a scribe line width extending in a first direction on the substrate first surface and a scribe line length extending in a second direction, perpendicular to the first direction, on the substrate first surface, the scribe line delineating a first region of the substrate from a second region of the substrate on the substrate first surface.
The substrate first surface is then optically scanned to locate the scribe line and determine a position of the scribe line. A first location on the substrate second surface is then marked with a first alignment mark by aiming a laser at the first location and firing the laser. The first alignment mark is then used to determine a position of the scribe line and align a laser beam with the scribe line using the alignment mark such that the laser beam is aligned on the second surface of the substrate with the scribe line on the first surface of the substrate. A trench is then created in the substrate using the laser.
According to the invention, the trench includes: a trench opening at the substrate second surface, the trench opening including a trench opening width extending in the first direction along the substrate second surface; a trench depth extending from the trench opening to a trench bottom located at a trench bottom position within the substrate, the trench bottom including a trench bottom width extending in the first direction at the trench bottom position within the substrate; first and second trench sides extending from the trench opening to the trench bottom; a trench length extending in the second direction on the substrate second surface and being at least partially coextensive with the scribe line length on the substrate first surface such that the trench is positioned below the scribe line within the substrate and the trench delineates the first region of the substrate from the second region of the substrate on the substrate second surface.
The first region of the substrate is then singulated from the second region of the substrate along the trench.
In accordance with a third embodiment of the present invention, a method includes providing a wafer, the wafer including a wafer first surface and a wafer second surface, opposite the wafer first surface, and a wafer thickness between the wafer first surface and the wafer second surface. A plurality of scribe lines is then formed on the wafer first surface, each of the scribe lines including a scribe line width extending in a first direction on the wafer first surface and a scribe line length extending in a second direction, perpendicular to the first direction, on the wafer first surface, the plurality of scribe lines delineating a plurality of regions on the wafer first surface.
A laser beam is then aligned on the wafer second surface such that the laser beam is aligned on the wafer second surface with one scribe line of the plurality of scribe lines on the wafer first surface. A trench is then created in the wafer second surface using the laser.
According to the invention the trench includes: a trench opening at the wafer second surface, the trench opening including a trench opening width extending in the first direction along the wafer second surface; a trench depth extending from the trench opening to a trench bottom located at a trench bottom position within the wafer, the trench bottom including a trench bottom width extending in the first direction at the trench bottom position within the wafer; first and second trench sides extending from the trench opening to the trench bottom; a trench length extending in the second direction on the wafer second surface and being at least partially coextensive with the scribe line length on the wafer first surface such that the trench is positioned below the scribe line within the wafer.
Then the aligning of the laser beam on the wafer second surface and creating a trench in the wafer second surface is repeated for each one of the plurality of scribe lines on the wafer first surface such that a plurality of trenches are created delineating a plurality of regions on the wafer second surface.
The plurality of regions are then singulated from the wafer along the trenches.